AdoHcy hydrolase has been cloned from several species and the properties of the enzymes have been studied. AdoHcy hydrolase from most species is a tetramer, and each monomer tightly binds NAD which is reduced and oxidized during the catalytic cycle. Mutagenesis studies have identified amino acids involved in binding of NAD and in inactivation of AdoHcy hydrolase. We obtained crystals from a solution of recombinant R. capsulatus AdoHcy hydrolase that was greater than 90% pure by SDS gel electrophoresis, and obtained x-ray diffraction data sufficient for structural determination. We have cloned the rat hydrolase gene, determined the transcription starts, sequenced the gene in its entirety, and analyzed its exon/intron structure. The 1.2 kb 5' DNA region was cloned into a reporter plasmid and analyzed in transiently transfected CHO cells. Deletion and mutagenesis analyses of the 5' DNA region indicated an active promoter that contained one critical SP1 site. A TATA-like sequence, TATTTAAA, found 23 bp upstream from the first transcription start was changed to GCAGGCCT without affecting promoter activity, indicating that for the hydrolase gene, TATTTAAA is not a functional TATA box.